II. Field of the Invention
The present invention relates to communication systems. More particularly, the present invention relates to a method and apparatus for providing power control in a dosed-loop communication system.
III. Description of the Related Art
The use of code division multiple access (CDMA) modulation techniques is one of several techniques for facilitating communications in which a large number of system users exist. Other multiple access communication system techniques, such as time division multiple access (TDMA) and frequency division multiple access (FDMA) are known in the art. However, the spread spectrum modulation techniques of CDMA has significant advantages over other modulation techniques for multiple access communication systems. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS," assigned to the assignee of the present invention, and is incorporated by reference herein. The use of CDMA techniques in a multiple access communication system is further disclosed in U.S. Pat. No. 5,103,459, entitled "SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM," also assigned to the assignee of the present invention, and is incorporated by reference herein.
CDMA by its inherent nature of being a wideband signal offers a form of frequency diversity by spreading the signal energy over a wide bandwidth. Therefore, frequency selective fading affects only a small part of the CDMA signal bandwidth. Space or path diversity is obtained by providing multiple signal paths through simultaneous links from a mobile user or mobile station through two or more cell-sites. Furthermore, path diversity may be obtained by exploiting the multipath environment through spread spectrum processing by allowing a signal arriving with different propagation delays to be received and processed separately. Examples of path diversity are illustrated in U.S. Pat. No. 5,101,501 entitled "METHOD AND SYSTEM FOR PROVIDING A SOFT HANDOFF IN COMMUNICATIONS IN A CDMA CELLULAR TELEPHONE SYSTEM," and U.S. Pat. No. 5,109,390 entitled "DIVERSITY RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEM," both assigned to the assignee of the present invention and incorporated by reference herein.
If the transmission power of signals transmitted by the base station to a mobile station are too high, it can create problems such as interfering with other mobile stations. As a result, most base stations have a fixed amount of power at which to transmit signals, and therefore can transmit to only a limited number of mobile stations. Alternatively, if the transmission power of signals transmitted by the base station are too low, then the mobile station can receive multiple erroneous transmitted frames. Terrestrial channel fading and other known factors can affect the transmission power of signals transmitted by the base station. As a result, each base station must rapidly and accurately adjust the transmission power for the signals which it transmits to the mobile stations. A method and apparatus for controlling transmission power is disclosed in U.S. Pat. No. 5,056,109, entitled "METHOD AND APPARATUS FOR CONTROLLING TRANSMISSION POWER IN A CDMA CELLULAR TELEPHONE SYSTEM," assigned to the assignee of the present invention and incorporated by reference herein.
The CDMA communication system can also exchange signals with fixed location stations. Such fixed stations typically employ directional antennas and thereby communicate with only certain sectors of one or more base stations. Fixed stations also typically lack fading concerns caused by movement of the station. Consequently, the fixed nature of such fixed stations, their directional antennas, as well as other factors, allow such stations to enjoy increased performance over mobile stations. Such fixed stations often operate as wireless local loops with their corresponding base stations, and thus require less overhead from the communication system. As a result, subscribers of fixed stations typically enjoy less expensive service.